JPS63171115A - Overload relay - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention provides a method for overloading electric equipment such as a transformer.
This invention relates to an overload relay that issues a load cutoff command so as not to impair the life of electrical equipment.

(Prior art) Conventionally, overload operation of oil-immersed transformers has been carried out based on certain guidelines (for example, see IEEJ Report (I) Part No. 99 (June 1970) "Oil-immersed Transformer Operating Guidelines"). This type of guideline considers the normal lifespan of transformers and life loss due to rises in transformer temperature due to overload operation.

When overloading a transformer, consideration is given to the above guidelines so as not to impair the normal lifespan of the transformer. Conventionally, overcurrent relays and timers are used to prevent overload conditions from occurring for a certain period of time or longer. If the problem continues, measures are taken to cut off the load.

(Problem to be solved by the invention) However, although the life loss due to overload operation depends on the load condition and ambient temperature, which change from time to time, it is possible to calculate the life loss by importing this data online. An overload relay that determines whether or not load shedding is possible by sequentially calculating has not yet been provided. Also,
As a recent trend, overload relays have been proposed that mainly focus on transformer temperature and ambient temperature to determine overload conditions, but they do not calculate the life loss itself, and furthermore, they do not calculate temperature at light loads. Because this is not done, there is a problem in that the actual life loss at light loads is not reflected in relay operation.

The present invention was proposed to solve the above-mentioned problems, and its purpose is to constantly capture the load status of electrical equipment such as transformers, and to detect the ambient temperature selected from the normal temperature data stored in memory. An object of the present invention is to provide an overload relay which outputs an appropriate load cutoff command by referring to the life loss in a microcomputer and enables overload operation without impairing the normal life of electrical equipment.

(Means for Solving the Problems) In order to achieve the above object, the present invention continuously calculates the life loss, which changes depending on the load of electrical equipment such as a transformer, using a microcomputer for each unit period. , in the overload relay that outputs the load cutoff command when the life loss exceeds the overload limit, the ambient temperature of the electrical equipment is selected from normal temperature data stored in advance in the memory, and the ambient temperature is The life loss is calculated in accordance with the highest point temperature within a unit period determined using .

Further, it is preferable to determine the remaining life of the electrical equipment by successively subtracting the life loss from the normalized initial life. Furthermore, it is desirable to divide one day into a plurality of parts according to the load curve of the electrical equipment, set an overload limit for each set time period, and manage the lifespan for each of these time periods.

(Operation) In the present invention, the ambient temperature corresponding to that point in time is selected and referenced from the normal temperature data in the memory for each unit period, and at the same time, the load current is taken in and the life loss is calculated from these. Then, this life loss is successively subtracted from the lifespan obtained by distributing the normal lifespan, which does not exceed the daily overload limit, to each time period, for example.

Further, when the life loss reaches a predetermined distributed life, the auxiliary relay is driven and a partial load cutoff command is output, thereby enabling overload operation within the normal life.

(Example) An embodiment of the present invention will be described below with reference to the drawings.

The figure schematically shows the configuration of the main part of the present invention. In the figure, TR is a transformer such as an oil-immersed transformer to be protected by the present invention, and the overload relay 1 according to the present invention is a transformer such as an oil-immersed transformer to be protected by the present invention. The load current of the device TR is input, and when the overload condition exceeds the limit, the auxiliary relay 6 is energized and a partial load cutoff command is output.

In the overload relay 1, 2 is an analog input section,
The analog input section 2 is connected to the secondary side of the current transformer CT that detects the load current of the transformer TR as described above.

This analog input section 2 is equipped with an A/D conversion section, and has an A/D conversion section.
The load current A/D converted by the A/D converter is input to the microcomputer 3.

The microcomputer 3 includes a calculation section, a memory 8, a digital input/output section, and the like. Of these, memory 8
In order to obtain the ambient temperature 0a(t) used for calculating the highest point temperature θh(t) of the transformer 1, as described later, the normal temperature data at the point where the transformer 1 is installed (transformer 1 If it is an outdoor type, outside temperature data) is stored. For example, this normal temperature data is obtained by taking 8 data every 3 hours per day and assuming that it changes in a yearly cycle (12 months), assuming that it does not change for a month, 8 x 12 = 96 data. It consists of Such normal temperature data can be easily obtained from meteorological observatories and the like.

The microcomputer 3 performs arithmetic processing, which will be described later, based on the load current and ambient temperature (normal temperature data) converted into digital signals, and activates the auxiliary relay 6 as necessary.
energize. Further, the microcomputer 3 is provided with a calendar 4 and a clock 5 for calculating month, day, and time, respectively. Note that 7 indicates a panel for operation.

Hereinafter, a method of controlling a load using this overload relay 1 will be described in detail.

First, the lifespan of transformer TR will be considered. The above-mentioned “
According to the "Oil-immersed Transformer Operating Guidelines," the normal lifespan of transformer TR is Y. is 30 years when operated at a maximum point temperature of 95°C, and the life Y of the transformer TR is as a function of the maximum point temperature Oh: Y = YoXexp, ((-b X (eh-95)
)−・・−・■ [Here, b=Un(2/6)). Therefore, when θh=95°C, Y=
30 years, when e h = 101℃ (e h -95
) is 6°C, so Y=30/2=15 years, e h
= When 89℃ (eh -95) is -6℃, so Y = 30X 2 = 60 years, when 0h = 91.5℃ (e h -95) is -3.5℃, so Y = 45 years.

Also, if eh is a function of time t, then unit period (unit time)
The life loss of the transformer TR per unit is -...
・・・・・・・・・・・・・・・・・・■.

From this, if the average value θh of the highest point temperature per unit period is obtained, the life loss V per unit period can be calculated. Here, for example, choose half a day as the unit period, and the average value θh = 101°C during the day and the average value θh = 89 at night.
If the operating temperature is 0.degree. C., the life will be lost twice as much during the day and the life will be gained twice as much during the night, compared to when operating at .theta.h=95.degree.

This is the average value for summer and winter, assuming the unit period is half a year.
The same applies when the values are different.

In this embodiment, the unit period is one second, and the life loss V is calculated sequentially based on the average value θh of the highest point temperature for each unit period. Here, the life loss V is expressed as normal life Y. There is also a method of using the ratio to -30 years (v x 1, and when ■ = 1, the life is reached), but here -'/- is the normal life per second of 1, as shown below. It is assumed that this will be consumed sequentially over a period of 30 years.

In other words, the normal lifespan Y. = 30 years = 10950 days =
Since the time is 946080000 seconds, the transformer TR is initially 9
It has a lifespan of 46080000 seconds, and e h =
If the temperature is maintained at 95 degrees Celsius and the device is operated, the lifespan will be lost at a rate of 1 per second, and after 30 years, the lifespan will reach Y20. Based on this idea, the normal life for 1 second is 1.1 minute is 60.1 hour is 3600.1 day is 86400. Here, for convenience of calculation, each number is multiplied by 10 and the normal lifespan of 1 second is 10.1 minute is 600.1 hour is 36000.1 day is 864000. . Therefore, the normal lifespan of 30 years (Y
o) becomes 9460800000.

The microcomputer 3 in the overload relay 1 calculates the highest point temperature 0h(t) at that point by starting a program once every second. The calculation formula is as follows.

θh=θa+θo1eg・・・・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・ ■In addition, in the formula ■, θo=eonX((K2R+1)/(R+1)e g=θgnXK", and =P/Pn. Among these variables, only the ambient temperature ea(t) and the actual load p(t) of the transformer are a function of time t; the others are determined by the transformer itself, so when applying the equation can be regarded as constants.

The actual load p (t) may be considered to be the load current I (t) under the condition that the rated voltage is constant, and this value is input to the analog input section 2 via the current transformer CT. In addition,
θa (t) is calculated from the calendar 4 by the microcomputer 3 itself from the normal temperature data in the memory as described above.
, refer to the clock 5 and sequentially select and use the one corresponding to the recognized time.

As a result, the microcomputer 3 can extremely accurately determine the highest point temperature eh(t) every second, and then calculates the life loss Vs per second at that point from this eh(t). The following equation, which is a modification of the 0 equation, is used for the calculation.

Vs=lOX2(en-gS)/6・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・ ■Table 1 below shows an example of the life loss Vs for each temperature eh calculated using this formula. In this table 1, ○h=95
At temperatures above °C, overload operation will occur.
This means that many times the normal lifespan is lost per second.

Table 1 Therefore, microcomputer 3 calculates 1 sequentially.
Life loss per second Vs is normal life Y per day. d=
By subtracting from 864,000, it is possible to detect moment by moment how much remaining life is left per day. Since the microcomputer 3 can determine the month, date, hour, and minute using the calendar 4 and the clock 5, the start of the daily life loss calculation may be set at 3:00 a.m. when the highest point temperature Oh is considered to be the lowest.

In this way, life loss calculation starts from 3:00 am, and Y
Subtract from od = 864000 and get Y o d
” When it reaches 0, it means that the standard life for that day has been used up, so after that, turn off the transformer T so that it does not take any load.
All that is required is to stop the operation of R, but in this example, taking into account circumstances such as the load curve of transformer TR during the day, the day is divided into multiple time periods as shown in Table 2. Y during these times. d: Distribute 864,000.

Table 2 Note that the settings of the time period, life allocation, constants of the transformer TR, etc. are performed via the panel 7 in the figure.

Therefore, the microcomputer 3 determines which of the above categories the current time belongs to, and subtracts the life loss calculated for each second within that category from the corresponding distributed life. The remaining life is displayed on the panel 7 or the like according to the above. Then, when the distribution life of the relevant section reaches O, the auxiliary relay 6 is energized to partially cut off the load.

Although the following second embodiment describes the case where the present invention is applied to an oil-immersed transformer, the present invention is not limited to this embodiment in any way, and the life loss per unit period is a function of temperature. Of course, it can be applied to other electrical equipment as well.

(Effects of the Invention) As detailed above, according to the present invention, the actual state of life loss and remaining life is calculated in extremely short cycles regardless of day or night, and the load on electrical equipment is appropriately adjusted based on the calculation results. Because of this control, it is possible to perform fine-grained overload operation according to the load characteristics of each device without impairing the normal lifespan of the electrical devices.

In particular, since the data in memory is used as the ambient temperature of electrical equipment used to calculate life loss, actual measurement with a thermometer etc. is not required, so a thermometer or A/D converter for temperature data is also unnecessary, simplifying the configuration. It is also possible to reduce costs.

[Brief explanation of the drawing]

The figure is a configuration diagram of main parts showing an embodiment of the present invention.

Claims (3)

[Claims] (1) A microcomputer continuously calculates the life loss that changes depending on the load of electrical equipment for each unit period, and when the life loss exceeds the overload limit, a command to cut off the load is output. In the load relay, the ambient temperature of the electric device is selected from normal temperature data stored in advance in a memory, and the life loss is calculated according to the highest point temperature within a unit period determined using this ambient temperature. An overload relay featuring: (2) The overload relay according to claim 1, wherein the remaining life is determined by sequentially subtracting the life loss from the normalized initial life of the electrical equipment. (3) The overload relay according to claim 1 or 2, wherein an overload limit is provided for each time period set by dividing one day into a plurality of periods.